Method for inferring the mechanical strain of GaN-on-Si epitaxial layers using optical profilometry and finite element analysis

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Spiridon, B. F. and Toon, M. and Hinz, A. and Ghosh, S. and Fairclough, S. M. and Guilhabert, B. J. E. and Strain, M. J. and Watson, I. M. and Dawson, M. D. and Wallis, D. J. and Oliver, R. A. (2021) Method for inferring the mechanical strain of GaN-on-Si epitaxial layers using optical profilometry and finite element analysis. Optical Materials Express, 11 (6). pp. 1643-1655. ISSN 2159-3930 (https://doi.org/10.1364/OME.418728)

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Abstract

GaN-on-Si has become a useful fabrication route for many GaN devices and applications, but the mechanical stress incorporated throughout the material stack can impact the viability of this approach. The transfer printing of GaN membrane devices, a promising emerging technology, is most effective with flat membranes, but in practice many GaN structures released from their Si substrate are highly bowed due to the strain in the epitaxial nitride stack. Our approach uses the optical profiles of epitaxial wafers and membranes as inputs for inferring the mechanical strain state of the material by multi-variable numerical model fitting using COMSOL Multiphysics. This versatile, adaptable and scalable method was tested on samples from two GaN-on-Si wafers, revealing the relationship between built-in strain and material bow in principal-component fashion, returning 3-4×10−4 strain estimates for the AlGaN (compressive) and GaN (tensile) layers, and suggesting the occurrence of plastic deformation during transfer printing.

ORCID iDs

Spiridon, B. F., Toon, M., Hinz, A., Ghosh, S., Fairclough, S. M., Guilhabert, B. J. E. ORCID logoORCID: https://orcid.org/0000-0002-3986-8566, Strain, M. J. ORCID logoORCID: https://orcid.org/0000-0002-9752-3144, Watson, I. M. ORCID logoORCID: https://orcid.org/0000-0002-8797-3993, Dawson, M. D. ORCID logoORCID: https://orcid.org/0000-0002-6639-2989, Wallis, D. J. and Oliver, R. A.;
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